Collator protocol validator side refactoring ideas

[tdimitrov]

For further refactoring:

• Let's avoid querying the per_relay_parent map again and again if we can pass it as a param to the function. it saves us some superfluous error handling that is already handled a level above. Originally posted by @alindima in Collation fetching fairness #4880 (comment)
• In Collations fetching_from really should be a part of the CollationStatus::Fetching() status variant Originally posted by @alindima in https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1860614933
• Avoid calculating claim queue state each time it is needed (unfulfilled_claim_queue_entries and the code in ensure_seconding_limit_is_respected). Instead keep ClaimQueueState for all paths in State, keep them up to date by marking seconded and pending canddiates accordingly, and have it ready for use when needed. - https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1861728429 and https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1861727967
• Consider moving the claim queue state checks in prospective parachains subsystem (by @Overkillus )

[alindima]

Generally it would also help if the code were less procedural and better structured in objects with methods

[alindima]

Also #6492

[alindima]

we should also rework the fetching timeouts. they are currently still firing even if the fetch was successful.
we probably also want to cancel the fetch if it timed out?